Hi, Elisabeth: Angie's shirt is from Banana Republic (I believe). That particular shirt is not available in petites in Canada. But they have other button front shirts that are. I find their petites fit me well. I own one of their sateen no -iron shirts and another shirt from last summer. I am about 5' 4" but short waisted. Around 115 with a small bust and narrow rib cage but relatively wide shoulders. (32/ 38.5) And I wear the 2 petite for a fitted style. Can get away with the 4 petite if the style is less fitted, but if it is meant to fit snug then that won't work for me. I haven't tried a 0 on, but I suspect it would be too tight. FWIW.
I can also sometimes wear x-small of their regular sizes. That seems shirt specific, and also depends on whether I will always roll or scrunch the sleeves. I do have a couple of their regular shirts in xs.
You can order and return free of charge, so these are worth trying, IMO. They are having a sale now.
You might also try J. Crew. I do not know the fit of theirs as well.
Another place to try might be Talbot's but I can't speak from any experience on that.
Hope this helps!